A Statistical Mechanical Model of Cholesterol/Phospholipid Mixtures: Linking Condensed Complexes, Superlattices, and the Phase Diagram

István P. Sugár, Parkson L.-G. Chong
2011 Journal of the American Chemical Society  
Despite extensive studies for nearly three decades, lateral distribution of molecules in cholesterol/ phospholipid bilayers remains elusive. Here we present a statistical mechanical model of cholesterol/phospholipid mixtures that is able to rationalize almost every critical mole fraction (X cr ) value previously reported for sterol superlattice formation as well as the observed biphasic changes in membrane properties at X cr . This model is able to explain how cholesterol superlattices and
more » ... sterol-phospholipid condensed complexes are inter-related. It gives a more detailed characterization of the LG I region (a broader region than the liquid disordered -liquid ordered mixed phase region), which is considered to be a sludge-like mixture of fluid phase and aggregates of rigid clusters. A rigid cluster is formed by a cholesterol molecule and phospholipid molecules that are condensed to the cholesterol. Rigid clusters of similar size tend to form aggregates, in which cholesterol molecules are regularly distributed into superlattices. According to this model, the extent and type of sterol superlattices, thus the lateral distribution of the entire membrane, should vary with cholesterol mole fraction in a delicate, predictable and non-monotonic manner, which should have profound functional implications. NIH Public Access
doi:10.1021/ja2092322 pmid:22196210 pmcid:PMC4120115 fatcat:lu34olimjfg6royyw2df3snhuy